Class 8 Science: Chapter-Wise Detailed Explanation [Updated]

Class 8 Science is the best standard to learn concepts about science. You can know about new scientific technologies which can help you understand the basics before you move towards the advance.

This article is especially for those who are eager to learn class 8 science. Today, I will show you each and every concept of class 8 science which can help you learn and make your basics stronger.

I have discussed each chapter and I will also take some exercises on each chapter so that you will be thoroughly prepared for your exams.

We are also going to add more practical examples which can help you think out of the box. I suggest you read each chapter in depth so that you won’t miss anything.

Lesson 1: Crop Production & Management

As the name suggests, the chapter is discussed about crop production. It is written about the definition of crops, its production and many more.

In simple terms, a crop is a plant which has been grown and developed at one place from a seed.

These crops are divided into two main types:-

  1. Kharif Crops
  2. Rabi Crops

Kharif Crops are crops which are planted in the rainy season.

Rabi Crops are crops which are planted in the winter season.

These were the two main types of crops. The next process is about the procedure for production of crops.

There is a certain process to produce a crop.

Class 8 science Crop Production process

This process clearly shows the crop production procedure.
Next we will discuss concepts related to soil preparation. Always approach loosened soil for the crop production process.
Loosened soil is always useful as it contains more worms and other organisms which help to strengthen the cropping process.
We cannot easily gain the loosened soil. You may have heard the process called ploughing.

Ploughing helps to loosen the soil which is required to plant the crops.

Plough is required for the process of ploughing.

plough

This is the plough used for ploughing. It helps to loosen the soil which is then used for crop production.

It is made of wood. Farmers pull it for ploughing.

The next part is planting the crops. This method is also called sowing. It is planting the seeds to grow.

You need to make sure that you are using premium quality seeds for crop production.
Also, take care to add enough fertilizer and nutrients to boost crop production and protect from insects.

Fertilizers help to add necessary nutrients to the soil like nitrogen to make the soil in good condition to produce more crops through less seeds.

Manure helps to improve the quality of soil and water holding capacity.  It also improves the soil texture which can help to improve the quality of soil to produce good quality crops.

Next step is to water these crops. This process is also called irrigation.

Irrigation is necessary because it avoids crops drying out and keeping them in good condition.

There are various sources to hydrate the crops like wells, through water pumps, rivers, dams, etc.

This is the irrigation process and sources to keep plants and crops in good condition.

Now, you have done everything right to grow your crop. The next step is to protect the plant and crops from insects and weeds.

Protecting the crops from insects and weeds is called weeding. There are various methods to control these weeds.

One of the popular methods is the chemical called weedicide. It protects the crops and plants from these weeds and grows the crop in good condition.

The crop is protected from insects and weeds. Now, you can move towards the next step that is harvesting!

Harvesting is the process of cutting the crops when they are ripened. You can cut these crops through a machine or manually.

There are unwanted things attached to the crops which are called chaff. The process of removing chaff from the crops is called threshing.

Last step is storage. The storage is important and it is necessary to protect the crops from insects and other microbes which can damage the crops.

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Class 8 Science Lesson 2: Microorganisms

Microorganisms are living organisms which are not visible to naked eye. You can easily view it with the help of a microscope. 

In this chapter, we will learn everything about microorganisms.

We have to study four main types of microorganisms:-

  1. Protozoa
  2. Bacteria
  3. Fungi
  4. Algae

There are viruses which originated in the cell causing common flu. It also causes serious diseases.

These are some of the images of microorganisms.

Protozoa

class 8 science microorganisms

Bacteria

bacteria

Fungi

class 8 science chapter 2

Algae

Algae

These were some of the examples of microorganisms. There are different microorganisms. The one which harms us and one which is friendly.

Harmful microorganisms grow in the environment or live in the human body.

Friendly microorganisms can be used as three types:-

  1. Household use
  2. Commercial use
  3. Medicinal use

Household use includes making bread, curd, etc. Commercial use includes production of alcohol, vinegar, etc.

Medicinal use includes creating medicines to cure human beings from various bacterial attacks.

These are also called antibiotics.

Another important use of these microbes is they actively fix nitrogen in the environment. Eventually, they boost the soil fertility and improve the soil condition.

As I have discussed earlier, there are good and bad microorganisms.

Let’s discuss harmful organisms to the environment and human body.

Microorganisms causing diseases to the human body are called pathogens.

There are various transmission mediums which can transmit bacteria to the human body.

One of the harmful diseases called Tuberculosis is caused by bacteria through air transmission.

Bacterial infection can also pass through water transmission.

Cholera and Typhoid are bacterial infections caused through water. 

These patients are recommended to maintain specific hygiene and drink boiled water.

There are certain viruses causing viral infection to the human body. They can transmit through air as well as water.

Chicken pox and Polio are viral infections causing harm to the human body. These viruses enter the body through air.

These infections can be avoided if vaccination is taken at the proper age.

Another viral infected disease is Hepatitis B. This is a water transmitted disease. One can drink boiled water to cure this disease.

These are viruses affecting the human body.

There are microbes affecting plants and animals. 

We will discuss more about plant diseases in this chapter.

Citrus Canker is the plant disease caused by bacteria through air. This disease damages the crops and makes them waste. This disease can be controlled by using chemicals to kill these bacteria infections.

Now, we have learned about various diseases. Let’s discuss food storage and measures to protect food from these microbes.

One can use common salt to preserve foods like meat and fish for more time.

Sugar reduces the bacterial growth in the food.
Before concluding this chapter, there is an important concept called Nitrogen Fixation.

About 78% share is of nitrogen in the atmosphere. Also, nitrogen is useful for the environment and soil. It improves the quality of soil and its fertility.

class 8 science book chapter 2

Lesson 3: Synthetic Fibre and Plastic

In the last chapter, we have learnt about microorganisms and its types. In this chapter, we will learn about different fibres and plastics.

There are natural fibres which consist of large units. These natural fibres in large units are called polymers.

Synthetic fibres and plastics are similar to natural fibres.

These polymers are made of each and every smaller unit. 

Fibres are obtained naturally from plants and animals. The fibres obtained from plants and animals are called natural fibres.

These natural fibres are processed or made by man. These are called synthetic fibres. 

These fibres are made from chemical processing. There are different chemical processing of petrochemicals used to make synthetic fibres.

Synthetic fibres have wide uses. These can be used as household use like buckets, synthetic ropes, etc.

These fibres can also be used in the aircraft industry, ships and spacecraft industry. Also, these synthetic fibres can be used in the medical industry.

These synthetic fibres are classified in four main types of fibres:-

  1. Rayon
  2. Nylon
  3. Polyester
  4. Acrylic

Rayon is made from chemical treatment or processing of wood pulp. Nylon is made from natural processing of coal, water and air. This synthetic fibre is called fully synthetic fibre. 

In earlier days, it was natural raw material to prepare various goods.

Polyester is easy to handle and is used in making various dress materials.
Acrylic is the last type which is made of synthetic fibre. 

There different fibres having different characteristics. Some of them have high strength whereas some have good liquid absorption capacity.

Some are strong and attractive, but expensive. Some have a natural ability to burn whereas some have high durability.

Plastics are like a synthetic fibre. There are two main types of plastics:-

  1. Thermoplastic
  2. Thermosetting

Plastics are less costly, strong and durable. They are also poor conductors of electricity.

It is recommended to use rubber or plastic foot wear while operating with electric cables.

Similarly, plastics are not easily degradable. They are harmful for the environment. 

They can be easily burned.But, the gases released after burning plastics are very poisonous in nature.

Class 8 Science Lesson 4: Metals & Non-metals

Last chapter was all about fibres and plastics. This chapter we will discuss metals and non-metals.

Before we move towards the properties of metals and non metals, it is necessary to know the difference between them.

Metals have lustre and they are good conductors of heat and electricity.

Non metals do not have lustre and they are poor conductors of heat and electricity.

Metals possess the ability of malleability. Malleability is the ability of material to be compressed to thin sheets.

Non metals do not possess this ability. Non metals are ruptured when it is compressed or beaten to form a sheet.

Metals also possess the ability of ductility. Ductility is the ability to use these metals into thin wires. 

Non metals are destroyed when tried to be drawn into a wire.

Some metals possess the property called sonorous. The ability of metal when they are striked.

Usually, metals are hard and lustrous. They also possess sonorous ability.

Properties of metals are not possessed by non metals.

There are different chemical properties of metals and non metals. Metal reacts with oxygen to form its oxide.

Metallic oxides are basic in nature. Non metal reacts with oxygen to form its oxide.

These non-metallic oxides are acidic.

metallic oxide

Iron is a metal. It reacts with oxygen in presence of water to form its oxide.

Non metallic oxide

Magnesium is non metal. It reacts with oxygen to form magnesium oxide. This reaction is balanced.

Metals react with water to form their hydroxides. Copper is a metal. When copper (Cu) reacts with moist air for more time, it forms copper hydroxide.

Similarly, non metals react with water to form their acids.

It is said that not all non metals react with water to form acids or hydroxides. The properties differ from each element.

Sulphur is a non-metal. When sulphur (S) reacts with water, it forms sulphurous acid.

The properties of metals and non metals differ when they react with acids and bases.

There are wide uses of metals and nonmetals in our everyday life.

We have learned the importance of crops in the first chapter. These non metals are used as a fertilizer to boost the growth of crops and plants.

These are also used to purify and filter the water. It has its uses in the medical industry

Non metals are used as antiseptic to apply on wounds to cure.

Lesson 5: Coal & Petroleum

Last chapter was about metals and non metals. Moving forward, let’s study about coal and petroleum.

Coal is black and hard. It is used in the cooking industry.

It is also used as fuel amd in thermal power industries.

There are various uses of coal. 

It was found that vegetation got buried inside the earth. It was then converted to coal.

This process of conversion from dead vegetation to coal is known as carbonisation.

Coal is processed from three main products:-

1. Coke

2. Coal Tar

3. Coal Gas

Coke is black in colour and porous in nature.

Coal tar is black thick liquid with a weird odour.

The gas released while processing the coal is called coal gas.

Petroleum is the raw material used to prepare petrol and diesel.

It is dark liquid having an unpleasant smell.

It consists of various substances like petrol, diesel, etc.

These various constituents have different uses.

Liquified petroleum gas (LPG) is used in the household and commercial industry.

Petrol is used in motor bikes, cars and most of the automobiles. 

Kerosene is used in the household industry as well as the aircraft industry.

Diesel is also used in the automobile industry. It is also used as a fuel in electric generators.

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Class 8 Science Lesson 6: Combustion & Flame

In the last chapter, we learned about coal and its uses. Also, we learned the process of obtaining petrol from petroleum.

In this chapter, let’s focus on combustion and flame.

You may know that whenever you burn any substance, the substance releases heat. This process of releasing heat when any substance reacts with oxygen is called combustion.

Also, it is necessary to remember that combustion is not possible without the presence of oxygen.

During combustion, the elements which react with oxygen release heat and light. This reaction of releasing heat after reacting with oxygen is called an exothermic reaction.

Every element starts to ignite with the lowest temperature. This lowest temperature is called ignition temperature.

This ignition temperature varies from element to element. It is seen that inflammable elements or substances have the lowest temperature of ignition.

Sometimes unnecessary fire or heat is released during the combustion process.

This can be controlled by eliminating those substances or catalysts which are triggering the fire production.

Usually, water is used to reduce the fire.

There are many types of combustion processes. 

In this chapter, we will learn about three main types of combustion process:-

  1. Rapid
  2. Spontaneous
  3. Explosion

This was a summary about combustion and its different processes. Now, we will study about flame.

There are three major types of flames:-

  1. Dark Zone
  2. Luminous Zone
  3. Non-luminous Zone

Different fuels have different costs and different efficiencies. There is no ideal fuel. But, an ideal fuel is considered to have the highest calorific value.

Efficiency of fuel is calculated in terms of calorific value. It is also expressed as KJ/kg.

Various harmful gases are released during incomplete combustion of fuel like carbon dioxide, carbon monoxide, etc.

These gases are poisonous in nature and cause harm to humans and the environment.

These gases are likely responsible for global warming. 

Global Warming increases the overall temperature of earth.

Lesson 7: Conservation of Plants & Animals

Wildlife sanctuary, park and biosphere reserve are names given to the areas meant for conservation and preservation of forest and wild animals.

Biodiversity refers to the variability of living organisms during a specific area.

Plants and animals of a specific area are known as the flora and fauna of that area. Endemic species are found only during a particular area.

Species are those which face the danger of extinction. The Red Data Book contains a record of the endangered species.

Migration is the phenomenon of movement of a species from its own habitat to another habitat for a specific period of time per annum for a selected purpose like breeding.

We should always save, reuse and recycle paper to save trees, energy and water. Reforestation is the restocking of destroyed forests by planting new trees.

Class 8 Science Lesson 8: Cell: Structure & Functions

All organisms are made from smaller parts called organs.Organs are made from still smaller parts. The smallest living a part of an organism may be a ‘cell’.

Cells were first observed in cork by Robert Hooke in 1665.Cells exhibit sort of shapes and sizes. Number of cells also varies from organism to organism.

Some cells are large enough to be seen with the unaided eye. Hen’s egg is an example.

Some organisms are single-celled, while others contain a sizable amount of cells.

The only cell of unicellular organisms performs all the essential functions performed by

a variety of cells in multicellular organisms. 

The cell has three main parts:-

(i) The cell membrane, 

(ii) Cytoplasm which contains smaller components called organelles, and 

(iii) The nucleus.

Nucleus is separated from cytoplasm by a nuclear membrane. Cells without well organised nucleus, i.e. lacking nuclear membrane, are called prokaryotic cells.

Plant cells differ from animal cells in having an additional layer around the cell wall termed cell membrane.

Coloured bodies called plastids are found in the plant cells only. Green plastids containing chlorophyll are called chloroplasts.

Plant cell features a big central vacuole unlike a number of small vacuoles in animal cells.

Lesson 9: Reproduction In Animals

There are two modes by which animals reproduce. These are: (i) amphimixis and (ii) agamogenesis .

Reproduction resulting from the fusion of male and female gametes is called sexual reproduction.

The reproductive organs within the female include ovaries, oviducts and uterus.

The reproductive organs in male include testes, sperm ducts and penis.

The ovary produces female gametes called ova and the testes produce male gametes called sperms.

The fusion of ovum and sperm is named fertilization. The embryo is called a zygote.

Fertilization that takes place inside the feminine body is named internal fertilization. This is observed in citizenry and other animals such as hens, cows and dogs.

Fertilization that takes place outside the feminine the body is named as external fertilization. This is observed in frogs, fish, starfish, etc.

The zygote divides repeatedly to offer rise to an embryo. The embryo gets embedded within the wall of the uterus for further development.

The stage of the embryo during which all the body parts that are identifiable are named foetus. Animals like citizenry , cows and dogs which give birth to young ones are called viviparous animals.

Animals like hen, frog, lizard and butterfly which lay eggs are called oviparous animals.

The transformation of the larva into an adult through drastic changes is named Metamorphosis.

The sort of reproduction during which only one parent is involved is named asexual reproduction. In hydra, new individuals develop from buds. This method of agamogenesis is named Budding.

Amoeba reproduces by dividing itself into two. This type of agamogenesis is named binary fission.

Class 8 Science Lesson 10: Reaching The Age of Adolescence

Humans become capable of reproduction after puberty sets in. Between the ages of 11 children are called adolescents.

The onset of puberty brings about growth of the reproductive organs. Hair grows at various places on the body. Breasts develop in girls and facial hair (moustache and beard) appear in boys. Voice of boys becomes hoarse as the voice box enlarges during adolescence.

Children gain height during adolescence. The onset of puberty and maturity of reproductive parts are controlled by hormones. Hormones are secretions of endocrine glands which pour them directly into the bloodstream.

Pituitary secretes hormones which include somatotropin and hormones that make other glands like the testes, ovaries, thyroids and adrenals, secrete hormones. Pancreas secretes insulin, thyroid produces thyroxine and adrenals produce adrenaline.

Testosterone is the male hormone and estrogen, the feminine hormone. The uterine wall in females prepares itself to receive the developing fertilised egg. Just in case there’s no fertilisation, the thickened lining of the uterine wall breaks down and goes out of the body along with blood. This is often called menstruation.

Sex of the unborn child depends on whether the zygote has XX or XY chromosomes. It is important to eat balanced food and maintain personal hygiene during adolescence.

Lesson 11: Force & Pressure

Class 8 Science Force & Pressure we will learn in more depth about force & pressure.

Force might be a push or a pull. A force arises thanks to the interaction between two objects.

Force has magnitude also as direction. A change within the speed of an object or the direction of its motion or both implies a change in its state of motion.

Force working on an object may cause a change in its state of motion or a change in its shape. A force can act on an object with or without being in touch with it.

Force per unit area is named pressure. Liquids and gases exert pressure on the walls of their containers. The pressure exerted by air around us is known as air pressure.

Class 8 Science Lesson 12: Friction

Friction opposes the relative motion between two surfaces in touch . It acts on both the surfaces.

Friction depends on the character of surfaces in contact. For a given pair of surfaces friction depends upon the state of smoothness of these surfaces.

Friction depends on how hard the 2 surfaces press together. Static friction comes into play once we attempt to move an object at rest.

Sliding friction comes with play when an object is sliding over another. Sliding friction is smaller than static friction. Friction is vital for several of our activities.

Friction are often increased by making a surface rough. The only of the shoes and therefore the tyres of the vehicles are treaded to extend friction. The friction is usually undesirable.

Frictions are often reduced by using lubricants. When one body rolls over another body, rolling friction comes into play. Rolling friction is smaller than the sliding friction. In many machines, friction is reduced by using ball bearings.

Fluid friction are often minimised by giving suitable shapes to bodies occupation fluids.

Lesson 13: Sound

Sound is produced by vibrating objects. In citizenry , the vibration of the vocal cords produces sound. Sound travels through a medium (gas, liquid or solid). It cannot travel in vacuum.

The eardrum senses the vibrations of sound, It sends the signals to the brain. This process is called hearing. The amount of oscillations or vibrations per the second is named the frequency of oscillation.

The frequency is expressed in hertz (Hz) Larger the amplitude of vibration, louder is the sound.

Higher the frequency of vibration, the upper is the pitch, and shriller is that the sound. Unpleasant sounds are called noise.

Excessive or unwanted sounds cause noise pollution. sound pollution may pose health problems for citizenry.

Attempts should be made to minimise noise pollution. Plantation on the roadside et al. can reduce sound pollution.

Class 8 Science Lesson 14: Chemical Effects of Electric Current

Some liquids are good conductors of electricity and some are poor conductors.

Most liquids that conduct electricity are solutions of acids, bases and salts. The passage of an electrical current through a conducting liquid causes chemical reactions.

The resulting effects are called chemical effects of currents. The method of depositing a layer of any desired metal on another material, by means of electricity is named electroplating.

Lesson 15: Some Natural Phenomena

Some objects are often charged by rubbing with other objects. There are two sorts of charges — positive charge and charge.

Like charges repel and in contrast to charges attract each other. The electrical charges produced by rubbing are called static charges.

When charges move, they constitute an electric current.An electroscope could also be wont to detect whether a body is charged or not.

The method of transfer of charge from a charged object to the world is named earthing. The method of electrical discharge between clouds and therefore the earth or between different clouds causes lightning.

Lightning strikes could destroy life and property.Lightning conductors can protect buildings from the consequences of lightning.

An earthquake may be a sudden shaking or trembling of the world. Earthquakes are caused by a disturbance deep inside the earth’s crust.

It’s impossible to predict the occurrence of an earthquake.Earthquakes tend to occur at the boundaries of earth’s plates. These boundaries are known as fault zones.

Destructive energy of an earthquake is measured on the Richter scale . An earthquake measuring 7 or more on the Richter scale can cause severe damage to life and property.

We should always take necessary precautions to protect ourselves from earthquakes.

Class 8 Science Lesson 16: Light

Light is reflected from all surfaces. Regular reflection takes place when light is incident on smooth, polished and regular surfaces.

Diffused/irregular reflection takes place from rough surfaces.

Two laws of reflection are:-

(i) The angle of incidence is adequate to the angle of reflection. 

(ii) Incident ray, reflected ray and therefore the normal drawn at the purpose of incidence to the reflecting surface, dwells an equivalent plane.

Image formed during a plane mirror undergoes lateral inversion. Two mirrors inclined to every other give multiple images.

Beautiful patterns are formed during a kaleidoscope due to multiple reflections. Sunlight, called white light, consists of seven colours.

Splitting of sunshine into its constituent colours is known as dispersion. Important parts of the attention are cornea, iris, pupil, lens, retina and nervus opticus.

A traditional eye can see nearby and distant objects clearly. Dim-sighted persons can read and write using the Braille system. Dim-sighted persons develop their other senses more sharply to enhance their interaction with their environment.

Lesson 17: Stars & The Solar System

The phases of the moon occur because we will see only a part of the moon which reflects the light of the Sun towards us.

Stars are celestial bodies that emit light of their own. Our sun is additionally a star. It is convenient to precise distances of stars in light years.

Stars appear to maneuver from east to west. The pole star appears to be stationary from the Earth, because it’s situated on the brink of the direction of the axis of rotation of the world.

Constellations are groups of stars that appear to form recognisable shapes. The system consists of eight planets and a host of asteroids, comets and meteors.

A body revolving around another body is named a satellite.Moon is the natural satellite of the world. Some planets even have natural satellites.

Venus is the brightest planet within the night sky. Jupiter is the largest planet of the solar system.

The synthetic satellites revolve around the Earth. they’re much closer than the moon. Artificial satellites are used for weather forecasting, long distance communication and remote sensing.

Class 8 Science Lesson 18: Pollution of Air & Water

This is the last chapter of class 8 science on pollution of air and water.

Pollution is the contamination of air by impurities which can have a harmful impact on the living organisms and therefore the non-living components.

Pollutants are the substances which contaminate air and water. Carbon monoxide gas , nitrogen oxides, carbon dioxide, methane and sulfur dioxide are the major pollutants of air.

Increasing levels of greenhouse gases like CO2 are resulting in heating. Pollution is that the contamination of water by substances harmful to life.

Sewage, agricultural chemicals and industrial waste are a number of the main contaminants of water. Water which is purified and fit drinking is known as potable water.

Water may be a precious natural resource . We must learn to conserve it.

These were all chapters of class 8 science. I hope you learned every concept from this explanation.

Comment your reviews about this explanation and you can also drop your questions and doubts in the comment section. I will solve all of your queries as soon as possible.

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